Information service to the home is a new field, enabled by the availability of storage and transmission technologies that can store and deliver data such as video and images at an affordable cost. One example of such a new service is video on demand, wherein a subscriber interacts with a remote video service to request the presentation of a particular movie or other video program on the subscriber's television. This interaction may be via a telephone or may be via the same settop terminal and cable that are used to bring cable television programming to the television.
One technology that contributes to improved home information service is video compression technology. Using video compression, a motion-picture video can be sent over a communications channel using only a fraction of the bandwidth of a conventional television channel. As a result, many more video channels can be carried over a given medium, such as modern television cable media, so that it is now possible to have private or semi-private video channels entering the home, in a manner similar to a home's telephone service.
One known technique for video compression is referred to as the Motion Picture Industry Group (MPEG) compression algorithm. In this algorithm, each frame of a motion-picture video is described either independently or as a change from a previously-displayed frame. Thus a video scene might be described by a single independent frame which shows the entire scene as it initially appears, followed by a long series of change frames which describe the changes in the scene as actors move, for example. Using such a technique, considerable channel bandwidth can be saved by eliminating the redundant transmission of unchanging elements of the scene.
The MPEG algorithm and similar algorithms are already in use in video information services. The MPEG algorithm is described in the following specifications: ISO/IEC 11172, Nov. 1991 (MPEG 1); and ISO/IEC WG11 N0501, July 1993 (MPEG 2). Both of these specifications are incorporated herein by reference. Also, C-Cube Inc. sells MPEG decoder chips having part nos. CL450 and CL950.
While video compression is thus enabling the creation of a new video transmission network, other techniques are being used to enable greater subscriber interaction with the video service. One method for enabling such interaction via the cable television system is to employ a series of graphical menus that are displayed on the TV screen. The subscriber interacts with these menus in a fashion similar to a computer user's interaction with so-called graphical user interfaces, which employ windows, dialog boxes, buttons, pull-down menus, and other features to present information and options to the user. The remote video service is responsible for controlling the display of these items on the screen, and for receiving and interpreting subscriber input to ascertain the subscriber's request.
Graphical user interfaces are particularly common on personal computers (PCs) and workstations, which generally have in them all of the graphic software and/or hardware required to perform the drawing tasks required by the interface. In contrast, graphical user interfaces are not as widely used for home information services. Such interfaces require both a considerable amount of storage, for graphical libraries, drawing software, etc., and also high information bandwidth between the graphics hardware and the display. These features are readily available in a PC without unduly increasing its overall cost. However, the addition of graphics software and/or hardware to a relatively inexpensive settop greatly increases its cost. For this reason, graphics hardware and software either are not provided in settops, or, when they are, have only limited functionality in order to minimize cost.
In the cable TV industry, dedicated channels presently deliver program guide background to the settop, and relevant text is then overlaid on the background to display program guides with some graphics, such as lines and colors. It is known to use graphical enhancement integrated circuits in the settop to provide shadows and other visual enhancements to the displayed image. However, this method is limited in that there is only one background, and the analog nature of the signal used to convey the background limits the amount of detail that can be sent to the settop. Furthermore, this method only permits text overlays, and therefore cannot produce a robust graphical user interface of the type referred to above.